Varying Anion Coordination in New Families of Dinuclear NiIILnIII Complexes: Zero Field Slow Relaxation of Magnetization and Theoretical Validations

Herein, we report the room-temperature synthesis, structural characterization, and magnetic performances of two new families of dinuclear NiII-LnIII complexes, [NiLn(HL)2(NO3)3]·nH2O·CH3CN (1a-1c) (n = 1 for Ln = Tb, and n = 1.5 for Dy and Ho) and [NiLn(HL)2(OAc)2(H2O)]Cl·5H2O (2a-2c) (Ln = Tb, Dy, and Ho), developed utilizing the ligand H2L (2-methoxy-6-[(E)-2'-hydroxymethyl-phenyliminomethyl]-phenol). Partial deprotonation of H2L in the reaction medium provided HL-, ideally suited for trapping NiII and selected 4f ions in its two adjacent pockets. X-ray structural characterization of complexes 1a-2c showed the preferential pinning of the octahedral NiII center by the imine N-donor alongside LnIII centers with a coordination number of nine in a muffin geometry. Both Dy analogs exhibited clear out-of-phase signals (1b and 2b; Ueff = 20 K and 18.7 K, respectively) in the absence of an external dc field in ac magnetic susceptibility measurements, whereas slow relaxation of magnetization was apparent under the optimal applied fields of 2 and 3 kOe for the Tb analogs (1a and 2a) and Ho analogs (1c and 2c), respectively. The analysis of static and dynamic magnetic properties was reinforced by thorough CASSCF-based computational analysis and density functional theory (DFT) calculations.